The present invention relates to a double-rack-and-pinion swinging apparatus.
A double-rack-and-pinion swinging apparatus has merits of an increase in working torque and absorption of backlash of a gear portion at a swinging end by applying air pressure such that pistons of a pair and facing each other are actuated in opposite directions to each other.
A perspective view showing an outward appearance of a prior-art double-rack-and-pinion swinging apparatus is shown in FIG. 3 and a conceptual rendering showing a structure of the apparatus is shown in FIG. 4.
In the swinging apparatus 31, first and second cylinder bores 33 and 34 of a pair are provided in parallel in a casing 32, first and second pistons 35 and 36 of a pair are housed for sliding in the cylinder bores, racks 35a and 36a are respectively provided to the respective pistons, and a pinion 37 is engaged with the racks. In the first cylinder bore 33 and the second cylinder bore 34, first pressure chambers 33a and 34a and second pressure chambers 33b and 34b into and from which pressure air is supplied and discharged are formed respectively on opposite sides of the pistons 35 and 36 of the pair.
To opposite ends of the casing 32, as shown in FIG. 3, end caps 41 and 42 are airtightly and detachably secured by a plurality of bolts 43 through sealing means 44 such as gaskets. Opposite ends of the cylinder bores 33 and 34 of the pair are closed with the end caps 41 and 42. In one end cap 41, first and second ports 45 and 46 for supplying and discharging pressure fluid to and from the pressure chambers 33a, 34a, 33b, and 34b in the first and second cylinder bores 33 and 34 are provided to directly communicate with the first pressure chambers 33a and 34a. 
In the casing 32, as shown in FIG. 4, two air flow paths 51 and 52 respectively communicating with the first and second ports 45 and 46 are provided to axially pass through the casing 32. In the other end cap 42, two air flow paths 53 and 54 connected to the flow paths 51 and 52 are provided. The air flow paths 53 and 54 are formed of grooves provided to a surface of the end cap 42 and packing 55 for sealing is provided to peripheries of the grooves. The two air flow paths 53 and 54 are respectively connected to the second pressure chamber 34b in the second cylinder bore 34 and the second pressure chamber 33b in the first cylinder bore 33.
Therefore, pressure air supplied from the first port 45 flows into the first pressure chamber 33a in the first cylinder bore 33 and flows into the second pressure chamber 34b in the second cylinder bore 34 through the flow paths 51 and 53 to drive the pistons 35 and 36 in opposite directions to each other. At this time, air in the second pressure chamber 33b in the first cylinder bore 33 is discharged from the second port 46 through the flow paths 54 and 52 together with air in the first pressure chamber 34a in the second cylinder bore 34.
If pressure air is supplied from the second port 46, the air flows into the first pressure chamber 34a in the second cylinder bore 34 and flows into the second pressure chamber 33b in the first cylinder bore 33 through the flow paths 52 and 54 to drive the pistons 35 and 36 in opposite directions to those in the above case. At this time, air in the second pressure chamber 34b in the second cylinder bore 34 is discharged from the first port 45 through the flow paths 53 and 51 together with air in the first pressure chamber 33a in the first cylinder bore 33.
Therefore, the pressure air is synchronously supplied and discharged to and from opposite end portions to each other of the pistons 35 and 36 of the pair. As a result, the pistons 35 and 36 of the pair are synchronously driven in opposite directions to each other.
The swinging apparatus is used in various manners in which a swinging rotary table 49 is mounted to an output shaft of the pinion 37 engaged with the pair of racks to change an orientation of a workpiece with the table 49 or chuck arms are directly mounted to the pistons 35 and 36 of the pair to chuck the workpiece with the chuck arms.
In such a prior-art double-rack-and-pinion swinging apparatus, however, because the plurality of flow paths 51 and 52 are formed in the casing 32 to axially pass through the casing and are connected to the respective pressure chambers 33b and 34b by the flow paths 53 and 54 provided to the end cap 42, structures of the flow paths are complicated, lengths of the holes are long, and processing for making the holes is troublesome. Moreover, because it is necessary to obtain space, thicknesses, and the like taken up by the respective flow paths 51, 52, 53, and 54 in the casing 32 and the end cap 42, the casing 32 and the end cap 42 are upsized and it is difficult to miniaturize a product.
The present invention has been accomplished to solve such problems and it is technical objects of the present invention to simplify structures of air flow paths connecting respective ports and pressure chambers and to miniaturize a double-rack-and-pinion swinging apparatus.
To achieve the above objects, according to the present invention, there is provided a double-rack-and pinion apparatus comprising, a casing, a flow path forming member mounted to a bottom of the casing, a first cylinder bore and a second cylinder bore provided in parallel with each other in the casing, a first piston and a second piston for sliding in the cylinder bores, racks provided to the respective pistons and a pinion engaged with the racks, first pressure chambers and second pressure chambers formed respectively on opposite sides of the respective pistons, a first flow port and a second flow port for supplying pressure fluid to the respective pressure chambers, and a first flow path connecting the first pressure chamber on one end of the first piston and the second pressure chamber on one end of the second piston and a second flow path connecting the second pressure chamber on the other end of the first piston and the first pressure chamber on the other end of the second piston, the first and second flow paths being formed between the bottom of the casing and the flow path forming member.
In the double-rack-and-pinion swinging apparatus of the present invention having the above structure, because the first flow path connecting the first pressure chamber on one end of the first piston and the second pressure chamber on one end of the second piston and the second flow path connecting the second pressure chamber on the other end of the first piston and the first pressure chamber on the other end of the second piston are formed between the bottom of the casing and the flow path forming member mounted to the bottom, it is unnecessary to provide the air flow paths to the end cap and the long air flow paths provided to the casing and extending in the axial direction of the cylinder bores are unnecessary unlike the prior-art apparatus.
Therefore, according to the present invention, the end caps can be omitted and the long air flow paths provided to the casing and extending in the axial direction of the cylinder bores are unnecessary. As a result, structures of the flow paths of the double-rack and-pinion swinging apparatus are simple and the swinging apparatus can be miniaturized.
In the present invention, it is preferable that the first flow path and the second flow path are formed of a plurality of grooves provided to at least one of the bottom of the casing and a surface of the flow path forming member and that the grooves have packing for sealing the flow paths at peripheries of the grooves.
In the swinging apparatus, the casing includes a plurality of through holes connecting the bottom of the casing and the respective pressure chambers and the first flow path and the second flow path and the respective pressure chambers are connected to each other through the through holes.
In the swinging apparatus of the present invention, it is preferable that opposite ends of the first and second cylinder bores are respectively closed with plugs, that the first port is formed in the plug on one end of the first cylinder bore, and that the second port is formed in the plug on one end of the second cylinder bore.